In the context of en:wikis (and similar online communities), constructionism and reductionism (which, in encyclopedia standards debate, become inclusionism and exclusionism or deletionism) are two competing (and frequently conflicting) theories which have been developed within wiki communities, as to how to best manage, edit, and cull the sometimes massive amounts of information that a wiki's users or editors may produce. The two competing theories, and the dynamic and tension between them, were first observed in the original en:WikiWikiWeb in 2000. Since then, the debate has spread to other wiki communities as well.

The debate between the two theories centers on whether (and when) content (or entire articles) in a wiki should be edited out or deleted. The debate is seldom centered on content which there is a community consensus (or clear community rules) as to whether or not it should exist; instead the debate typically centers on content which is borderline--that which is considered valuable and useful by some; but as superfluous, "cruft", and "noise" by others.

Constructionism (often referred to as wiki constructionism or WikiConstructionism in camel case) is the theory that "the primary way to increase the quality of (a) Wiki is to add good content. Deleting noise can certainly help (although it's hard to do without causing damage), but it's no replacement for working hard to write valuable material." [1]. Constructionists hold that deleting material is a violent act--as it deprives members of the community who would prefer to keep the content the ability to read and improve it. Thus, is argued by the constructionist, wiki communities should err on the side of keeping material which is of a questionable nature.

Reductionism (or wiki reductionism or WikiReductionism) is (according to a description on WikiWikiWeb) the theory that for the "for Wiki quality to recover and then increase, Wiki could use quite a lot more deletion". [2] Reductionists argue that the perceived quality of a wiki is more closely correlated with the perceived quality of the individual articles therein, rather than the quantity; and thus conclude that articles or content which is of dubious quality should be removed, especially if it is unlikely that further editing or refactoring will improve the actual or perceived quality. A common analogy used is that of a decorative shrub; with careful pruning, the bush can be made into a work of art. Left unattended, however, it will grow into into an ummanageable brambles, unappealing and useful to nobody. The analogy fails to take into account dimensionality. A common term used within wiki communities for a coordinated attempt to find remove "deadwood" is a forest fire (the term is also used to mean a rapidly-expanding flamewar).

Some other techniques for resolving this debate have been proposed and/or implemented.

Filtering

Filtering is the use of technological measures to screen out content which is deemed to be dubious; such as contributions by a particular user or on a particular topic. Use of filters with other types of online forums and social software is a longstanding practice, going back to USENETkillfiles. Many weblogs and online forum provide content rating systems, where users can vote on or recommend particular articles and/or users. However, implementing such a scheme in a freely-editable medium such as a wiki has proven to be more difficult than in forums where each user's contributions are identified as their own, and users (other than moderators or sysops) cannot alter the contributions of others.

Use of an alternative namespace or site

Some wikis provide alternative namespaces or cites for content which is deemed to be inappropriate, off-topic, or of lower quality.

WikiWikiWeb is the original wiki, having been started in 1995. Its preferred topic has long been people, projects, and patterns, though today any discussion related to computer science and/or programming (as well as related disciplines such as mathematics) is generally considered to be "on-topic". WikiWikiWeb has numerous debates (and several edit wars) over the constructionist vs reductionist controversy over its nearly 11 years in existence. The first major incident on WikiWikiWeb occurred in 2000, when a group of editors one night deleted a significant amount of material from the site. [3]. This action was extremely controversial. The terms "reductionist" and "constructionist" were coined out of the ensuing debate.

One interesting outgrowth of the debate on WikiWikiWeb is the existence and development of so-called "sister sites". Several notable wikis, most importantly MeatballWiki, were created when large bodies of content on WikiWikiWeb (which were outside WikiWikiWeb's charter) were moved to a new and independent wiki. A more recent (and controversial) sister site of wiki is "The Adjunct", which is intended to hold any content deemed off-topic on c2.[4]

The English language edition of the online encyclopedia, Wikipedia, is the largest wiki site in the world. With over 3.7 million pages in its "article namespace" (and several times that in other namespaces), Wikipedia dwarfs all other wikis in both size and scope. The purpose of Wikipedia is to generate an encyclopedia; to that end Wikipedia permits articles on most any subject; but Wikipedia policy requires articles to be verifiable, exclude original research, and maintain a "neutral point of view". Unlike many wikis, the MediaWiki software on which Wikipedia runs does not permit ordinary users to delete pages; only administrators have sufficient privilege to do so. Excluding uncontroversial cases, deletion of a Wikipedia article requires a process known as Articles for deletion (or AfD) be undertaken, requiring that a consensus of Wikipedia editors demonstrate support for deletion of the article.

Within Wikipedia, the two philosophies are better known as inclusionism and deletionism, though some argue that a more accurate term for the latter philosophy is exclusionism. The debate primarily manifests itself on Wikipedia as a debate over precisely which subjects ought to be included in the encyclopedia. One of the site's policies is Wikipedia is not a paper encyclopedia, explaining that there is "no practical limit to the number of topics we can cover other than verifiability and the other points presented on this page." Many editors often argue that the very definition of an encyclopedia implies some level of editorial discretion in excluding what is viewed as superfluous or trivial articles. Debates over notability have been ongoing, with advocates of AfDs for articles which they consider to be dubious having been accused of pursuing a "exclusionist" (or more pejoratively, a "deletionist") agenda.

Several whole classes of articles have (among many others) been subjects of controversy. Extensive collections of articles on fictional universes--often derided by critics as "fancruft"--have been questioned, though Wikipedia currently has extensive documentation on epic fictional works such as the Lord of the Rings trilogy and the Star Wars saga. Another class of articles which has raised some eyebrows are a collection of pages maintained by so-called road geeks, documenting the highway system(s) of the world in great detail.